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  • 1
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    Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Biogeosciences, American Geophysical Union (AGU), 129(3), ISSN: 2169-8953
    Details
    Publication Date: 2024-02-27
    Description: Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO〈jats:sub〉2〈/jats:sub〉 and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO〈jats:sub〉2〈/jats:sub〉 sink with lower net CO〈jats:sub〉2〈/jats:sub〉 uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO〈jats:sub〉2〈/jats:sub〉 sink was located in western Canada (median: −52 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH〈jats:sub〉4〈/jats:sub〉 m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO〈jats:sub〉2〈/jats:sub〉 and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Decadal-scale hotspot methane ebullition within lakes following abrupt permafrost thaw (2021)
    Institute of Physics Publishing
    In:  EPIC3Environmental Research Letters, Institute of Physics Publishing, 16, pp. 035010-035010, ISSN: 1748-9326
    Details
    Publication Date: 2024-01-30
    Description: Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide (CO2) and methane (CH4) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH4 ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH4 ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release 14C-depleted CH4 from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH4 hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older 14C ages of CH4 released from hotspot seeps in older, expanding thermokarst lakes (14CCH4 20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger 14CCH4 in new lakes (14CCH4 8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger 14C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH4-hotspot seep emissions following formation of thermokarst lakes as climate warms.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 3
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    Earlier snowmelt may lead to late season declines in plant productivity and carbon sequestration in Arctic tundra ecosystems (2022)
    In:  EPIC3Scientific Reports, 12(1), ISSN: 2045-2322
    Details
    Publication Date: 2024-04-19
    Description: Arctic warming is affecting snow cover and soil hydrology, with consequences for carbon sequestration in tundra ecosystems. The scarcity of observations in the Arctic has limited our understanding of the impact of covarying environmental drivers on the carbon balance of tundra ecosystems. In this study, we address some of these uncertainties through a novel record of 119 site-years of summer data from eddy covariance towers representing dominant tundra vegetation types located on continuous permafrost in the Arctic. Here we found that earlier snowmelt was associated with more tundra net CO2 sequestration and higher gross primary productivity (GPP) only in June and July, but with lower net carbon sequestration and lower GPP in August. Although higher evapotranspiration (ET) can result in soil drying with the progression of the summer, we did not find significantly lower soil moisture with earlier snowmelt, nor evidence that water stress affected GPP in the late growing season. Our results suggest that the expected increased CO2 sequestration arising from Arctic warming and the associated increase in growing season length may not materialize if tundra ecosystems are not able to continue sequestering CO2 later in the season.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
    Electronic Resource
    Electronic Resource
    The HCO2 potential energy surface: Stationary point energetics and the HOCO heat of formation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5138-5140 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energies of six stationary points on the OH+CO→HOCO→H+CO2 potential energy surface have been calculated using the G3 and CBS-QB3 methods. An analysis combining ab initio and experimental enthalpies yielded ΔHf298 K (trans-HOCO)=−42.9±1.5 kcal mol−1 (−43.8±1.4 kcal mol−1) at the G3(CBS-QB3) level of theory. These results confirm the revised HOCO heat of formation derived from photoionization spectroscopy and suggest that the HOCO potential well is 8.8 kcal mol−1 shallower than previously thought. We discuss the implications of these results for accurate Rice–Ramsperger–Kassel–Marcus modeling or quantum mechanical scattering calculations of the OH+CO reaction. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1312824
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  • 5
    Electronic Resource
    Electronic Resource
    The OBrO C(2A2)←X(2B1) absorption spectrum (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2300-2307 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The highly structured visible absorption spectrum of the bromine dioxide radical, OBrO, has been observed in the 15 500–26 000 cm−1 region. The spectrum is dominated by a long progression in the Br–O symmetric stretching motion (ν1′) and a series of short progressions built on the bending mode (ν2′); there are no features associated with the excitation of the antisymmetric stretching mode (ν3′). The spectrum also contains numerous transitions originating from the (0,1,0) and (1,0,0) vibrational levels of the electronic ground state, X(2B1). A simultaneous fit to all of the observed vibronic features yielded the frequencies ν1″=799.4 cm−1, ν2″=317.5 cm−1, ω1′=641.5 cm−1, ω2′=210.7 cm−1, and a band origin T0=15 863 cm−1. Franck–Condon simulations combined with ab initio calculations of the four lowest OBrO doublet electronic states identify the spectrum as arising from the C(2A2)←X(2B1) electronic transition. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474606
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  • 6
    Electronic Resource
    Electronic Resource
    The rotational spectrum and molecular properties of bromine dioxide, OBrO (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8292-8302 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational spectrum of the OBrO radical has been observed in the gas phase over the solid products of the O+Br2 reaction. Spectra have been measured for both O79BrO and O81BrO in their (000), (010), and (020) vibrational states in selected regions between 88 and 627 GHz spanning the quantum numbers 1≤N≤61 and 0≤Ka≤14. The spectra are well described by a Hamiltonian which includes centrifugal distortion effects for fine and hyperfine terms. The molecular structure, the dipole moment, and the harmonic force field have been derived, and they, as well as fine and hyperfine structure constants, are compared with data of related molecules and electron spin resonance data from OBrO isolated in cryogenic salt matrices. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475030
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  • 7
    Electronic Resource
    Electronic Resource
    Pressure dependence and metastable state formation in the photolysis of dichlorine monoxide (Cl2O) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2857-2868 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO. Under these conditions, a weak, highly structured absorption spectrum was observed in the range 16 600–26 000 cm−1 with a lifetime on the order of 500 ms. A portion of the spectrum could be analyzed (22 000–26 000 cm−1) which showed progressions having differences of 283, 443, and 505 cm−1. Ab initio calculations were performed to evaluate vertical excitation energies and oscillator strengths from the lowest-energy singlet (X 1A1) or triplet (1 3B1) states to various excited states. The calculations indicated that the 2 3A2←1 3B1 transition has an unusually large oscillator strength. The transition energy, 3.05 eV, is consistent with the observed metastable spectrum. The observed pressure dependence of ClO formation could be modeled using a mechanism which assumed that Cl2O excitation at wavelengths longer than about 300 nm leads to rapid intersystem crossing to two metastable states in the triplet manifold. These states undergo competitive dissociation to ClO+Cl and collisional relaxation to the ground state. The dynamics of Cl2O may serve as a model for other molecules of importance in the earth's lower stratosphere such as ClONO2 where filtering of the solar spectrum by ozone restricts photolysis to the weak tail of the absorption continuum. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471109
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  • 8
    Electronic Resource
    Electronic Resource
    Slow electron transfer between main-group species: oxidation of nitrite by chlorine dioxide (1988)
    s.l. : American Chemical Society
    Inorganic chemistry 27 (1988), S. 4277-4280 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00296a039
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  • 9
    Electronic Resource
    Electronic Resource
    Rotational spectroscopy of IO X 2Πi (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6459-6470 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Pure rotational spectra of the IO radical have been observed for vibrational levels up to v=13 in the X1 2Π3/2 state and up to v=9 in the X2 2Π1/2 state. Isotopically enriched I18O rotational spectra have been observed for vibrational levels up to v=5 in both the X1 and X2 states. These are the first high-resolution spectra of any kind reported for the X2 state and greatly extend the available data for the X1 state. The data for both isotopomers have been fitted simultaneously to a single set of 2Π parameters with fixed isotopic ratios. The isotope relations among the parameters have provided a means of decorrelating the electron spin-rotation constant γ from the fine-structure centrifugal distortion constant, AD, and have allowed the first determination of an effective value for γ. The rotation–vibration constants correspond to the equilibrium molecular properties re(X1)=186.762 pm, re(X2)=188.468 pm, ωe(X1)=681.69 cm−1, and ωe(X2)=645.29 cm−1. These constants have been used to calculate X1 and X2 Rydberg–Klein–Rees potentials encompassing energies up to 40% of the dissociation limit. A complete set of hyperfine coupling constants has been determined for the first time and interpreted using appropriate relativistic atomic radial integrals. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398308
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  • 10
    Electronic Resource
    Electronic Resource
    Determination of microstructure and composition in butadiene and styrene-butadiene polymers by near-infrared spectroscopy (1990)
    s.l. : American Chemical Society
    Analytical chemistry 62 (1990), S. 1778-1785 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00216a010
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